The present invention relates to an apparatus and method for decontaminating the microspheres used to fluidize a fluidized patient support system.
An improved fluidizable patient support system such as disclosed in U.S. Pat. No. 4,564,965 to Goodwin (hereafter referred to as the Goodwin bed), which is hereby incorporated herein by reference, includes a tank for containing a mass of granular material, preferably ceramic spheres, also referred to as microspheres or beads. These beads have diameters on the order of 50 to 150 microns (10.sup.-6 meters). A perforated plate provides a false bottom for the tank and together with the bottom and sides of the tank define a plenum. A diffuser board, which is permeable to the flow of air but not to the beads, rests atop the perforated plate and isolates the beads from the plenum. A flexible sheet is removably secured around the upper edges of the tank, and the sheet is permeable to air and liquid but not to passage of the beads therethrough.
When the Goodwin bed is in use, body fluids of the patient and other contaminants pass through the sheet and contaminate the beads. The contaminants cause beads to aggregate into clumps and thereby lessen the efficiency of the fluidization process of the bed. In addition, the contaminants present problems of sanitation and the increased risk of infection with diseases.
The beads periodically must be decontaminated. One method of decontamination requires removing the beads from the Goodwin tank and passing the beads through a sieve to remove the clumps of contaminated material and aggregations of beads from the mass of individual beads. An elongated immersion heater is inserted into the Goodwin tank, and the sieved beads are returned to the tank. The mass of beads is fluidized by the passage of ambient air therethrough, and the immersion heater is operated to heat the beads to a temperature of 55.degree. C. The beads are continuously fluidized and maintained at a temperature no less than 55.degree. C. for 24 hours.
The above method using the Goodwin bed was modified by running the immersion heater at higher temperatures for shorter periods of time. For example, only 12 hours was required if the beads were maintained at a temperature no less than 65.degree. C., 8 hours for a temperature no less than 70.degree. C., 4 hours for a temperature no less than 75.degree. C., 4 hours for a temperature no less than 80.degree. C., 2 hours for a temperature no less than 85.degree. C., and 1 hour for a temperature no less than 90.degree. C.
The use of the above described apparatus is not without its problems. For example, the beads are poor conductors of heat, and those in the vicinity of the immersion heater become too hot and fuse together. Accordingly, the attainment of the higher temperatures necessary for reducing the time required for complete decontamination, exacerbates the bead fusion problems. The fused beads render the fluidization process less efficient and impair the heat distribution efficiency of the decontamination process. These inefficiencies require lengthening the duration of the decontamination process and reduce the advantage of running the immersion heater at higher temperatures.
In addition, maintaining the higher temperatures with the immersion heater often proved difficult or impossible. Significant heat losses are inherent in the Goodwin tank. Attaining the decontamination temperatures and maintaining them over the specified time periods required large energy expenditures and constant monitoring by service personnel. This was a particular problem during winter in many of the service centers performing the decontamination method situated in colder climates and in those service centers which were not well heated.
After the heat treatment portion of the decontamination process is completed, the beads must be allowed to cool to about 40.degree. C. before they can be handled. Cooling the beads takes a significant amount of time. This is especially true when the higher temperatures are attained during the heat treatment and even when the lower temperature heat treatment is carried out during summer months at service centers located in warmer climates. Since the decontamination units are occupied while the beads are cooling, the cooling phase prevents other lots of beads from being decontaminated and reduces the overall efficiency of the service center performing the decontamination process.
Furthermore, the technicians operating the Goodwin bed apparatus sometimes came into contact with the beads being decontaminated due to leakage of beads from the beds into the external environment. Constant monitoring by personnel continued to be required to ensure that at no time during the decontamination period does the temperature fall below the required minimum.